ring of life

Examples of ring of life in the following topics:

• Web, Network, and Ring of Life Models

  • To more accurately describe the phylogenetic relationships of life, web and ring models have been proposed as updates to tree models.
  • The "ring of life" is a phylogenetic model where all three domains of life evolved from a pool of primitive prokaryotes .
  • This does not mean a tree, web, or a ring will correlate completely to an accurate description of phylogenetic relationships of life.
  • According to the "ring of life" phylogenetic model, the three domains of life evolved from a pool of primitive prokaryotes.
  • Describe the web, network, and ring of life models of phylogenetic trees

• Properties of Aromatic Compounds

  • Aromatic compounds are cyclic structures in which each ring atom is a participant in a$\pi$ bond, resulting in delocalized $\pi$ electron density on both sides of the ring.
  • Due to this connected network of $\pi$ bonds, the rings are planar, unlike the boat or table structures typical of cycloalkanes.
  • Aromatic compounds are also interesting because of their presumed role in the origin of life as precursors to nucleotides and amino acids.
  • Benzene can only be fully depicted with all of its resonance structures, which show how its pi-electrons are delocalized throughout its six-carbon ring.
  • The reaction preserves the pi system of electrons and therefore the aromatic character of the benzene ring.

• Electrocyclic Reactions

  • An electrocyclic reaction is the concerted cyclization of a conjugated π-electron system by converting one π-bond to a ring forming σ-bond.
  • The electrocyclic ring closure is is designated by blue arrows, and the ring opening by red arrows.
  • The second diagram below shows two examples of thermal electrocyclic opening of cyclobutenes to conjugated butadienes.
  • This mode of reaction is favored by relief of ring strain, and the reverse ring closure (light blue arrows) is not normally observed.
  • Photochemical ring closure can be effected, but the stereospecificity is opposite to that of thermal ring opening.

• Cycloalkanes

  • Cycloalkanes have one or more rings of carbon atoms.
  • The simplest examples of this class consist of a single, unsubstituted carbon ring, and these form a homologous series similar to the unbranched alkanes.
  • Since all the carbons of a ring are equivalent (a ring has no ends like a chain does), the numbering starts at a substituted ring atom.
  • The molecular formulas of such compounds have H/C ratios that decrease with the number of rings.
  • The structural relationship of rings in a polycyclic compound can vary.

• Newton's Rings

  • Newton's rings are a series of concentric circles centered at the point of contact between a spherical and a flat surface.
  • Newton's rings appear as a series of concentric circles centered at the point of contact between the spherical and flat surfaces.
  • When viewed with monochromatic light, Newton's rings appear as alternating bright and dark rings; when viewed with white light, a concentric ring pattern of rainbow colors is observed.
  • An example of Newton's rings when viewed with white light is shown in the figure below .
  • The radius of the Nth bright ring is given by:

• Hydrocarbons

  • Hydrocarbons are important molecules that can form chains and rings due to the bonding patterns of carbon atoms.
  • As the backbone of the large molecules of living things, hydrocarbons may exist as linear carbon chains, carbon rings, or combinations of both.
  • This three-dimensional shape or conformation of the large molecules of life (macromolecules) is critical to how they function.
  • Another type of hydrocarbon, aromatic hydrocarbons, consists of closed rings of carbon atoms.
  • Ring structures are found in hydrocarbons, sometimes with the presence of double bonds, which can be seen by comparing the structure of cyclohexane to benzene .

• Cycloalkanes

  • Like alkanes, cycloalkanes are not particularly reactive, with the exception of the smallest, most strained cycloalkanes.
  • Cycloalkanes are composed of sp3 hybridized carbon and hydrogen atoms connected by sigma bonds.
  • When naming substituted cycloalkanes, the ring positions are numbered to minimize the numbering of the appended groups.
  • The rings of cycloalkanes have two faces, and substituent groups can be appended to either face.
  • The first image represents the chair configuration of cyclohexane, while the second represents the boat configuration.

• Configurational Stereoisomers of Cycloalkanes

  • Unlike the relatively flat molecules of alkenes, substituted cycloalkanes must be viewed as three-dimensional configurations in order to appreciate the spatial orientations of the substituents.
  • By agreement, chemists use heavy, wedge-shaped bonds to indicate a substituent located above the average plane of the ring (note that cycloalkanes larger than three carbons are not planar), and a hatched line for bonds to atoms or groups located below the ring.
  • In general, if any two sp3 carbons in a ring have two different substituent groups (not counting other ring atoms) stereoisomerism is possible.
  • Four other examples of this kind of stereoisomerism in cyclic compounds are shown below.
  • If more than two ring carbons have different substituents (not counting other ring atoms) the stereochemical notation distinguishing the various isomers becomes more complex.

• Beta-Lactam Antibiotics: Penicillins and Cephalosporins

  • The β-lactam ring is part of the core structure of several antibiotic families.
  • A β-lactam (beta-lactam) ring, is a four-membered lactam .
  • The β-lactam ring is part of the core structure of several antibiotic families, the principal ones being the penicillins, cephalosporins, carbapenems, and monobactams, which are, therefore, also called β-lactam antibiotics.
  • Nearly all of these antibiotics work by inhibiting bacterial cell wall biosynthesis.
  • Cephalosporins are indicated for the prophylaxis and treatment of infections caused by bacteria susceptible to this particular form of antibiotic.

• Steroids

  • The four rings are designated A, B, C & D as noted, and the peculiar numbering of the ring carbon atoms (shown in red) is the result of an earlier misassignment of the structure.
  • This is shown in the last of the toggled displays, along with the preferred conformations of the rings.
  • For purposes of discussion, the left ring is labeled A (colored blue) and the right ring B (colored red).
  • Each of the angular hydrogens (Hae or Hea) is oriented axial to one of the rings and equatorial to the other.
  • The fusion of ring C to ring B in a trans configuration prevents ring B from undergoing a conformational flip to another chair form.